[Gllug] Recommend an ADSL modem?

[Nix]

On Sat, 24 Jan 2004, dylan at dylan.me.uk moaned:
> On Saturday 24 January 2004 16:54 pm, Doug Winter wrote:
>> Gah, so what's a half-bridge?
> 
> I've just set this up myself, so hopefully I understand what's going on 
> now...

Remember: it is always nastier than you think.

(But in this case, not much nastier.)

> The ADSL modem assigns its external IP address to the internal 
> router/gateway, and simply passes all packets through. In a full 
> bridge, you need to do the PPPoA/PPPoE on the gateway, but with a half 
> bridge the modem does that for you.

i.e., it bridges layer 3, but *not* layer 2. Since most of us don't want
to piss about with PPPoAnything this is generally a good idea.

> You only need to set up the routing table on the gateway with the 
> relevant settings, which I managed to work out by trial and error from 
> the modem's route table.

The Conexant firmware is much more `amusing' than that.

To get it working, you have to do this:

- flick on `PPP half bridging'
- reboot the router
- after the line has come up, get the IP address for the router-side
  of your firewall's network interface via DHCP. (If you do it too
  early, the router will assign you a rubbish one, and you'll pretty
  much have to reboot. You can't tell whether you've rebooted too
  soon without doing it, so I use an exponential-backoff reboot-and-
  try-again scheme for that delay too.)
- the lease time on that IP address is one minute, and if you miss
  it the router goes dumb and refuses to talk to you.
- if another DHCPDISCOVER is broadcast after you've got that IP
  address, the router goes dumb again.

Argh gak.

-- 
`note to the crown prosecution service: Machine guns dont have a
 'stun' setting.' --- mjw
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